The present invention relates to a control system for a vehicular braking system incorporating a hydrodynamic brake and a friction brake acting in parallel, wherein the brake pedal force or the brake pedal position is utilized to indicate the required total brake torque and the required total brake torque is generated by the hydrodynamic brake with first priority with the friction brake being controlled such that it generates the difference between the required total brake torque and the brake torque provided by the hydrodynamic brake.
Control systems of this type are known and in practical use. A problem of such control systems is that the friction brake, as a result of physical conditions, responds earlier than the hydrodynamic brake and, accordingly, is subject to a substantial amount of wear. Further, the efficiency of the hydrodynamic brake is substantially ensured in higher speed ranges only whereas the friction brake is fully operable in both higher and lower speed ranges.
In order to ensure an optimum efficiency of control systems including a hydrodynamic brake combined with a friction brake, the requirement is for the friction brake to respond under no circumstances above a specific or threshold vehicle speed from which the hydrodynamic brake possesses the necessary effectiveness, nor shall the friction brake respond at the beginning of a braking action, provided the hydrodynamic brake is in a position to provide the wheel deceleration required for the individual case. If the hydrodynamic brake does not provide, or provides only partially, the wheel deceleration corresponding to the brake pedal force applied, the friction brake is required to supply the missing share. Finally, at speeds below the above-mentioned threshold speed and at which the effectiveness of the hydrodynamic brake decreases as a result of the physical conditions and/or a defect, the friction brake has to compensate for the missing or required deceleration share.